Using dispersed queues for rebuilding functions and prioritization

ABSTRACT

A method includes scanning, by a scanning module, from plurality of sets of encoded data slices to plurality of sets of encoded data slices, to identify encoded data slices that are in need of rebuilding. The method further includes adding, by the scanning module, the identified encoded data slices into a first level rebuilding queue. The method further includes analyzing, by an analyzing module, the identified encoded data slices based on a rebuilding prioritization function to establish a prioritization for the identified encoded data slices. The method further includes transferring, by the analyzing module, a first group of encoded data slices into a first priority rebuilding queue and a second group of encoded data slices into a second priority rebuilding queue based on the analyzing. The method further includes rebuilding, by a rebuilding module, the first and second group of encoded data slices based on a rebuilding prioritization protocol.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility patent application claims priority pursuant to35 U.S.C. §120 as a continuation-in-part of U.S. Utility applicationSer. No. 14/055,174, entitled “ACCESSING DISTRIBUTED COMPUTING FUNCTIONSIN A DISTRIBUTED COMPUTING SYSTEM”, filed Oct. 16, 2013, which claimspriority pursuant to 35 U.S.C. §119(e) to U.S. Provisional ApplicationNo. 61/733,686, entitled “GENERATING A DISPERSED QUEUE”, filed Dec. 5,2012, all of which are hereby incorporated herein by reference in theirentirety and made part of the present U.S. Utility patent applicationfor all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention relates generally to computer networks and moreparticularly to dispersing error encoded data.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

As is further known, over time, data may become corrupted or outdated,and may not be able to be reproduced once a certain amount of the dataincludes an error. For example, in a RAID 5 system with 3 disks, if morethan one disk fails, entire arrays of data may be unrecoverable.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of an embodiment of rebuildingencoded data slices in accordance with the present invention;

FIG. 10 is a schematic block diagram of an example of determiningprioritization of encoded data slices in accordance with the presentinvention;

FIG. 11 is a flowchart illustrating an example of a method of rebuildingencoded data slices in accordance with the present invention;

FIG. 12 is a schematic block diagram of another embodiment of adispersed storage network (DSN) in accordance with the presentinvention; and

FIG. 13 is a flowchart illustrating an example of queuing a rebuildingtask in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 & 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data as subsequently described with reference to oneor more of FIGS. 3-8. In this example embodiment, computing device 16functions as a dispersed storage processing agent for computing device14. In this role, computing device 16 dispersed storage error encodesand decodes data on behalf of computing device 14. With the use ofdispersed storage error encoding and decoding, the DSN 10 is tolerant ofa significant number of storage unit failures (the number of failures isbased on parameters of the dispersed storage error encoding function)without loss of data and without the need for a redundant or backupcopies of the data. Further, the DSN 10 stores data for an indefiniteperiod of time without data loss and in a secure manner (e.g., thesystem is very resistant to unauthorized attempts at accessing thedata).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSTN memory 22for a user device, a group of devices, or for public access andestablishes per vault dispersed storage (DS) error encoding parametersfor a vault. The managing unit 18 facilitates storage of DS errorencoding parameters for each vault by updating registry information ofthe DSN 10, where the registry information may be stored in the DSNmemory 22, a computing device 12-16, the managing unit 18, and/or theintegrity processing unit 20.

The DSN managing unit 18 creates and stores user profile information(e.g., an access control list (ACL)) in local memory and/or withinmemory of the DSN memory 22. The user profile information includesauthentication information, permissions, and/or the security parameters.The security parameters may include encryption/decryption scheme, one ormore encryption keys, key generation scheme, and/or dataencoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particularuser, a user group, a vault access, public vault access, etc. Forinstance, the DSTN managing unit 18 tracks the number of times a useraccesses a non-public vault and/or public vaults, which can be used togenerate a per-access billing information. In another instance, the DSTNmanaging unit 18 tracks the amount of data stored and/or retrieved by auser device and/or a user group, which can be used to generate aper-data-amount billing information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSTN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 60 is shown inFIG. 6. As shown, the slice name (SN) 60 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a schematic block diagram of an embodiment of rebuildingencoded data slices in a dispersed storage network (DSN). The DSNincludes a DSN memory 22, a scanning module 90, a 1^(st) levelrebuilding queue 92, an analyzing module 94, a 1^(st) priority queue 96,a 2^(nd) priority queue 98, a 3^(rd) priority queue 99, and a rebuildingmodule 100. Note one or more of the scanning module 90, the analyzingmodule 94 and the rebuilding module 100 may be implemented within acomputing device or within multiple computing devices. As one example, afirst computing device includes the scanning module 90, a secondcomputing device includes the analyzing module 94, and a third computingdevice includes the rebuilding module 90. As another example, a firstcomputing device includes the scanning module 90, the analyzing module94 and the rebuilding module 100. As yet another example, a firstcomputing device includes the scanning module 90, and a second computingdevice includes the analyzing module 94 and the rebuilding module 100.

In an example of operation, the scanning module 90 scans a plurality ofsets of encoded data slices that are stored in DSN memory 22 to identifyencoded data slices that need rebuilding (e.g., missing, outdatedversion, flagged, etc.). For example, the scanning module sends listrequests to storage units of the DSN that include a request to listslice names of encoded data slices being stored by the respectivestorage units. The scanning module 90 then receives list responses fromthe storage units that include a list of slices names of encoded dataslices that are stored by the respective storage units. The scanningmodule then interprets the list of slices names of encoded data slicesthat are stored by the respective storage units to identify the encodeddata slices that need rebuilding.

Continuing with the example of operation, when the scanning module 90identifies encoded data slices for rebuilding, the scanning module 90adds the identified encoded data slices to the 1^(st) level rebuildingqueue 92. As an example, the scanning module 90 scans a first set ofencoded data slices and determines that a fifth encoded data slice ofthe first set is corrupted (e.g., a computed slice name does not match astored slice name) and an eighth encoded data slice of the first set ismissing (e.g., the storage unit did not respond with a slice name forthe eighth encoded data slice). The scanning module 90 then adds thefifth and eighth encoded data slices to the 1^(st) level rebuildingqueue 92.

As encoded data slices for rebuilding are added to the 1^(st) levelrebuilding queue 92, the analyzing module 94 analyzes the encoded dataslices of the 1^(st) level rebuilding queue 92 based on a rebuildingprioritization function to establish a priority level for at least someof the identified encoded data slices. For example, during a firsttimeframe, the 1^(st) level rebuilding includes eight encoded dataslices for rebuilding. The analyzing module analyzes the eight encodeddata slices for rebuilding based on the rebuilding prioritizationfunction and determines that a first group of four encoded data slicesare of a first priority, that a second group of three encoded dataslices are of a second priority, and a third group of one encoded dataslice is of a third priority. Having determined the priorities, theanalyzing module transfers the first group to the first priority queue96, the second group to the second priority queue 98 and the third groupto the third priority queue 99.

After transferring at least one group of encoded data slices to one ofthe priority queues, the rebuilding module 100 rebuilds encoded dataslices of the at least one group in accordance with a rebuildingprioritization protocol. Note the rebuilding prioritization protocolcomprises one of rebuilding the first group of encoded data slicesbefore rebuilding the second group of encoded data slices, rebuildingthe first and second group of encoded data slices in an imbalanced roundrobin manner that favors rebuilding the first group of encoded dataslices, and rebuilding the first and second group of encoded data slicesin accordance with an anti-starvation protocol.

For example, the rebuilding module 100 may rebuild all encoded dataslices in the first priority queue 96 before rebuilding any encoded dataslices in the second priority queue 96. As another example, therebuilding module 100 may rebuild in a round robin fashion such that forevery four encoded data slices that are rebuilt in the first priorityqueue 96, two encoded data slices are rebuilt in the second priorityqueue 98, and one encoded data slice is rebuilt in the third priorityqueue 99. As yet another example, the rebuilding module 100 may spend80% of time rebuilding encoded data slices of the 1^(st) priority queue96, 15% of time rebuilding encoded data slices of the 2^(nd) priorityqueue 98 and 5% of time rebuilding encoded data slices of the 3^(rd)priority queue 99. After rebuilding the encoded data slices forrebuilding, the rebuilding module 100 sends the rebuilt encoded dataslices 102 to DSN memory 22 for storage.

FIG. 10 is a schematic block diagram of an example of determiningprioritization of encoded data slices. The encoded data slices and addto priority queues in accordance with the prioritization. The priorityqueues include 1^(st) priority queue 96, 2^(nd) priority queue 98, and3^(rd) priority queue 99. Note that although three priority queues areillustrated, there may be less or more priority queues in otherembodiments.

As illustrated, a first and a second set of encoded data slices areassociated with a first data object with dispersed storage error encodedparameters that include a pillar width (e.g., n) of 7 and a decodethreshold (e.g., k) of 4, and a third set of encoded data slices isassociated with a second data object with dispersed storage errorencoded parameters that include a pillar width of 12 and a decodethreshold of 5.

The shaded encoded data slices are encoded data slices that are in needof rebuilding (e.g., corrupted, outdated, flagged, etc.). For example,in the first set of encoded data slices of the first data object (e.g.,EDS 1_1 through EDS 7_1), encoded data slices EDS 5_1, EDS 6_1, and EDS7_1 need rebuilding, in the second set of encoded data slices of thefirst data object (e.g., EDS 1_2 through EDS 7_2), encoded data sliceEDS 3_2 need rebuilding, and in the third set of encoded data slices ofthe second data object (e.g., EDS 1_4 through EDS 12_4), encoded dataslice EDS 9_4 needs rebuilding. The analyzing module 94 module analyzesthe encoded data slices that need rebuilding based on a rebuildingprioritization function to establish a prioritization for at least someof the identified encoded data slices (e.g., EDS 5_1, EDS 6_1, EDS 7_1,EDS 3_2 and EDS 9_4).

In this example, the analyzing module determines EDS 5_1 and EDS 6_1 area first priority, EDS 7_1 and EDS 3_2 are a second priority, and EDS 9_4is a third priority. The rebuilding prioritization function thatestablishes the priorities may be based on a loss of data risk analysisfunction that is executed on a set of encoded data slices by set ofencoded data slices basis. The loss of data risk may be determined byone or more of a pillar number, a decode threshold number, a number ofencoded data slices in a set of encoded data slices that needrebuilding, and a storage unit reliability.

For example, the first set of encoded data slices (EDS 1_1-EDS 7_1) hasa pillar width of 7, a decode threshold of 4 and 3 encoded data slicesthat need rebuilding. Thus, as the first set of encoded data slices cantolerate loss of another encoded data slice, at least one of the encodeddata slices (e.g., EDS 5_1, EDS 6_1, EDS 7_1) should be given thehighest priority. Note that within the highest priority, one or more ofthe encoded data slices may have a higher priority. For example,initially EDS 5_1, EDS 6_1 and EDS 7_1 would all be included in thefirst priority, however, once EDS 5_1 has been rebuilt, EDS 6_1 willhave a lower loss of data risk as the first set may now tolerate failureof one encoded data slice. Further, once EDS 5_1 and 6_1 are bothrebuilt, the loss of data risk will be lower as the first set of encodeddata slices may now tolerate two failures and still be recoverable.Thus, EDS 7_1 may instead be determined to have a second priority, whichis lower than the first priority. In this example EDS 7_1 and EDS 3_2are of the second priority, however the priority for EDS 7_1 may behigher than EDS 3_2, even though the slice risk value (e.g., differencebetween the redundancy value (e.g., a difference between the pillarnumber and the decode threshold number) and the number of encoded dataslices in the set of encoded data slices that are in need of rebuilding)are substantially similar. In one example, this may be due to a storageunit reliability level of a storage unit storing an encoded data sliceof the second set of encoded data slice being higher that a storage unitreliability level of a storage unit storing an encoded data slice of thefirst set of encoded data slices. Thus, the first set of encoded dataslices has a higher loss of data risk than the second set of encodeddata slices.

The third set of encoded data slices includes a pillar width of 12, adecode threshold of 5 and 1 encoded data slice that needs rebuilding.Thus, at this time, the third set could tolerate failure of up to sixencoded data slices and still be recoverable. As such, EDS 9_4 may bedetermined to have a low rebuilding priority (e.g., a third priority)and thus may be transferred to the 3^(rd) priority queue 99.

FIG. 11 is a flowchart illustrating an example of a method of rebuildingencoded data slices. The method begins with step 110, where a scanningmodule of a computing device scans, from one or more plurality of setsof encoded data slices to other one or more plurality of sets of encodeddata slices, to identify encoded data slices that need rebuilding. As anexample of the scanning, the scanning module sends list requests tostorage units of the DSN, that include a request to list slice names ofencoded data slices being stored by the respective storage units. Next,the scanning module receives list responses from the storage units thatinclude a list of slices names of encoded data slices that are stored bythe respective storage units. The scanning module then interprets thelist of slices names of encoded data slices that are stored by therespective storage units to identify the encoded data slices that needrebuilding.

The method continues with step 112, where the scanning module adds theidentified encoded data slices into a first level rebuilding queue. Themethod continues with step 114, where an analyzing module of a computingdevice analyzes identified encoded data slices in the first levelrebuilding queue based on a rebuilding prioritization function toestablish a prioritization for at least some of the identified encodeddata slices in the first level rebuilding queue. Note the prioritizationfunction includes a loss of data risk analysis function that is executedon a set of encoded data slices by set of encoded data slices basis.

For example, for a set of encoded data slices of the one or moreplurality of sets of encoded data slices or of the other one or moreplurality of sets of encoded data slices, the analyzing moduledetermines a pillar number, a decode threshold number, a number ofencoded data slices in the set of encoded data slices that are in needof rebuilding and determines a redundancy value based on a differencebetween the pillar number and the decode threshold number. Next, theanalyzing module determines a slice risk value based on a differencebetween the redundancy value and the number of encoded data slices inthe set of encoded data slices that are in need of rebuilding anddetermines storage unit reliability of a set of storage units of the DSNthat is storing the set of encoded data slices. Having determined theslice risk value and the storage unit reliability, the analyzing modulegenerates a loss of data risk indication based on the slice risk valueand the storage unit reliability. When the loss of data risk indicationis above a threshold, the analyzing module places one or more encodeddata slices of the set of encoded data slices that need rebuilding inthe first group of encoded data slices.

When the at least some of the identified encoded data slices in thefirst level rebuilding queue are of a first priority, the methodcontinues with step 116, where the analyzing module transfers a firstgroup of encoded data slices in the first level rebuilding queue into afirst priority rebuilding queue based on the analyzing.

When the at least some of the identified encoded data slices in thefirst level rebuilding queue are of a second priority, the methodcontinues with step 118, where the analyzing module transfers a secondgroup of encoded data slices in the first level rebuilding queue into asecond priority rebuilding queue based on the analyzing. Note the firstrebuilding priority queue has priority over the second priorityrebuilding queue.

The method continues with step 120, where a rebuilding module of acomputing device rebuilds the first and second group of encoded dataslices based on a rebuilding prioritization protocol. As an example ofthe rebuilding, the rebuilding module may determine whether the time torebuild the first group of encoded data slices will exceed a priorityrebuild time threshold. When the time to rebuild the first group ofencoded data slices will exceed the priority rebuild time threshold, therebuilding module allocates a sub-group of the first group of encodeddata slices to a second rebuilding module for rebuilding. Note thesecond rebuilding module may be operable on the first computing device,the second computing device, the third computing device, or a fourthcomputing device of the one or more computing devices. Further note, therebuilding prioritization protocol includes one of rebuilding the firstgroup of encoded data slices before rebuilding the second group ofencoded data slices, rebuilding the first and second group of encodeddata slices in an imbalanced round robin manner that favors rebuildingthe first group of encoded data slices, and rebuilding the first andsecond group of encoded data slices in accordance with ananti-starvation protocol.

In one instance, when an encoded data slice has been in a lower prioritygroup (e.g., the second group, the third group, etc.) of encoded dataslices for a predetermined period of time, the encoded data slice may bere-analyzed based on the rebuilding prioritization function to determinewhether the encoded data slice should be moved to a higher prioritygroup (e.g., the first group) of encoded data slices. When it isdetermined to move the encoded data slice to the first group of encodeddata slices, a computing device (e.g., the analyzing module 94, therebuilding module 100) transfers the encoded data slice to the firstgroup of encoded data slices.

FIG. 12 is a schematic block diagram of another embodiment of adispersed storage system that includes one or more dispersed storage(DS) unit sets 520, 502, a scanning module 522, and a rebuilding module524. Each DS unit set of the one or more DS unit sets 520, 502 includesa set of DS units 504. In a first embodiment, as illustrated, the one ormore DS unit sets are implemented as two DS unit sets 520, 502.Alternatively, in another embodiment, the one or more DS unit sets areimplemented as a common DS unit set. The scanning module 522 and therebuilding module 524 may be implemented utilizing one or more of a userdevice, a server, a processing module, a computer, a DS processing unit,a DS processing module, a DS unit, a distributed storage and task (DST)processing unit, a DST processing module, a DST client module, and a DSTexecution unit. For example, the scanning module 522 is implemented in afirst DST execution unit and the rebuilding module 524 is implemented ina second DST execution unit. As another example, the scanning module 522and the rebuilding module 524 are implemented utilizing a common DSTexecution unit.

The system functions to detect one or more stored slices in error (e.g.,missing and/or corrupted slices that should be stored in one or more DSunits 504 of a first DS unit set 520) and to remedy (e.g., rebuild) theone or more stored slices in error. The scanning module 522 functions todetect the one or more stored slices in error and the rebuilding module524 functions to remedy the one or more stored slices in error. Thescanning module 522 communicates identities of the one or more storedslices in error to the rebuilding module 524 by utilizing entries of adispersed queue. A second DS unit set 502 of the one or more DS unitsets is utilized to provide the dispersed queue.

The scanning module 522 functions to detect the one or more storedslices in error and to update the dispersed queue with an entrypertaining to at least one stored slice in error. The scanning module522 functions to detect the one or more stored slices in error through aseries of steps. A first step includes generating a set of list requests526 that include a range of slice names to be scanned associated withthe first DS unit set. A second step includes outputting the set of listrequests 526 to the first DS unit set 520. A third step includescomparing list slice responses 528 from the first DS unit set 520 toidentify one or more slice names associated with the one or more storedslices in error. For example, the scanning module 522 identifies a slicename that is not listed in a list response when slice names of a set ofslice names that are associated with the slice name are received viaother list responses.

The scanning module 522 functions to update the dispersed queue througha series of steps. A first step includes assigning a rebuilding prioritylevel for the slice in error. A second step includes generating a queueentry that includes one or more of the slice name, the rebuildingpriority level, a rebuilding task indicator, and identity of the set ofslice names that are associated with the slice name (e.g., a sourcename). A third step includes identifying the dispersed queue based onone or more of the source name, the rebuilding priority level, arebuilding module availability level indicator, and a queue availabilitylevel indicator. A fourth step includes storing the queue entry in theidentified dispersed queue associated with the second DS unit set. Thestoring includes encoding the queue entry to produce a set of entryslices, identifying a rebuilding dispersed queue, generating a set ofentry slice names for the queue entry, generating a set of write queueentry requests 530 that includes the set of entry slices and the set ofentry slice names, and outputting the set of write queue entry requests530 to the second DS unit set 502.

The rebuilding module 524 functions to remedy the one or more storedslices in error through a series of steps. A first step includesretrieving a queue entry from a highest priority dispersed queue fromthe second DS unit set 502. The retrieving includes outputting a set ofqueue entry requests 532 that includes a set of list requests associatedwith a slice name range of the highest priority dispersed queue,receiving a set of queue entry responses 534 that includes a set of listresponses, identifying a set of slice names associated with the queueentry (e.g., lowest slice names of a range of slice names associatedwith a first in first out (FIFO) approach), generating and outputting aset of delete read slice requests that includes the set of slice namesto the second DS unit set 502, receiving at least a decode thresholdnumber of entry slices from another set of queue entry responses 534,and decoding the at least a decode threshold number of entry slices toproduce the queue entry.

A second step to remedy the one or more stored slices in error includesextracting the slice name of the slice in error from the queue entry(e.g., the queue entry including a distributed computing function torebuild and the slice name). A third step includes facilitatingrebuilding of the slice in error (e.g., directly rebuilding, issuing arebuilding request to another rebuilding module). When directlyrebuilding, the rebuilding module 524 outputs, to the first DS unit set520, at least a decode threshold number of read slice requests 536 thatincludes slice names associated with the slice in error, receives atleast a decode threshold number of read slice responses 538 thatincludes slices associated with the slice in error, decodes the slicesassociated with the slice in error to produce a recovered data segment,and encodes the recovered data segment to produce a rebuilt slice. Afourth step includes generating and outputting, to the first DS unit set520, a write slice request 540 that includes the slice name of the slicein error and the rebuilt slice. A fifth step includes receiving a writeslice response 542 that includes status of writing the rebuilt slice.

When the status of writing the rebuilt slice is favorable (e.g.,succeeded), the rebuilding module 524 generates and outputs, to thesecond DS unit set 502, a set of queue entry requests 532 that includesa set of commit requests associated with the delete read requestspreviously output to the second DS unit set 502 with regards toretrieving the queue entry. Such a set of requests 532 completesdeletion of the queue entry to remove the queue entry from the dispersedqueue since the slice in error has been successfully rebuilt.

FIG. 13 is a flowchart illustrating an example of queuing a rebuildingtask. The method begins at step 544 where a processing module (e.g., ofscanning module) identifies a slice name of a slice in error of a set ofslices stored in a set of dispersed storage (DS) units. The identifyingincludes generating and outputting, to the set of DS units, a set oflist slice requests to include a slice name range to be scanned forerrors, receiving list slice responses, and identifying the slice nameof the slice in error based on a comparison of list slice responses. Themethod continues at step 546 where the processing module determines arebuilding priority level. The priority level may be based on one ormore of a number of slice errors associated with a common set of slices,a vault identifier, a data type indicator, a source name of the commonset of slices, and a data priority level. For example, a higherrebuilding priority level may be assigned when the number of sliceerrors associated with a common set of slices is greater than a slicethreshold level.

The method continues at step 548 where the processing module generates aqueue entry that includes the slice name of the slice in error, arebuilding task indicator (e.g., a rebuilding opcode), identity of theset of slices (e.g., the source name of the common set of slices), andthe rebuilding priority indicator. The method continues at step 550where the processing module identifies a rebuilding queue based on therebuilding priority indicator. The identifying may include one or moreof a lookup (e.g., a queue list by rebuilding priority level), a query,and receiving. The method continues at step 552 where the processingmodule facilitates storing the queue entry in the identified rebuildingqueue in another set of DS units. Alternatively, the processing modulefacilitates storage of the queue entry in the identified rebuildingqueue in the set of DS units.

The facilitating storage of the queue entry in the identified rebuildingqueue includes a series of steps. A first step includes generating a setof queue entry slice names based on one or more of a queue vaultidentifier, a queue name associated with the identified rebuildingqueue, a DS processing module identifier associated with the processingmodule, a client identifier based on a vault lookup, and a currenttimestamp. A second step includes encoding the queue entry using adispersed storage error coding function to produce a set of queue entryslices. A third step includes generating a set of write slice requeststhat includes the set of queue entry slices and the set of queue entryslice names. A fourth step includes outputting the set of write slicerequests to the other set of DS units when utilizing the other set of DSunits for storage of the queue entry.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method for execution by one or more computingdevices in a dispersed storage network (DSN), the method comprises:scanning, by a scanning module of a first computing device of the one ormore computing devices, from one or more plurality of sets of encodeddata slices to other one or more plurality of sets of encoded dataslices, to identify encoded data slices that are in need of rebuilding;adding, by the scanning module, the identified encoded data slices intoa first level rebuilding queue; analyzing, by an analyzing module of thefirst computing device or a second computing device of the one or morecomputing devices, the identified encoded data slices in the first levelrebuilding queue based on a rebuilding prioritization function toestablish a prioritization for at least some of the identified encodeddata slices in the first level rebuilding queue; transferring, by theanalyzing module, a first group of encoded data slices in the firstlevel rebuilding queue into a first priority rebuilding queue based onthe analyzing; transferring, by the analyzing module, a second group ofencoded data slices in the first level rebuilding queue into a secondpriority rebuilding queue based on the analyzing, wherein the firstrebuilding priority queue has priority over the second priorityrebuilding queue; and rebuilding, by a rebuilding module of the firstcomputing device, the second computing device, or a third computingdevice of the one or more computing devices, the first and second groupof encoded data slices based on a rebuilding prioritization protocol. 2.The method of claim 1, wherein the scanning comprises: sending, by thescanning module, list requests to storage units of the DSN, wherein thelist requests include a request to list slice names of encoded dataslices being stored by the respective storage units; receiving, by thescanning module, list responses from the storage units, wherein the listresponses includes a list of slices names of encoded data slices thatare stored by the respective storage units; and interpreting, by thescanning module, the list of slices names of encoded data slices thatare stored by the respective storage units to identify the encoded dataslices that are in need of rebuilding.
 3. The method of claim 1, whereinthe rebuilding prioritization function comprises: a loss of data riskanalysis function that is executed on a set of encoded data slices byset of encoded data slices basis.
 4. The method of claim 3 furthercomprises: for a set of encoded data slices of the one or more pluralityof sets of encoded data slices or of the other one or more plurality ofsets of encoded data slices: determining a pillar number, a decodethreshold number, a number of encoded data slices in the set of encodeddata slices that are in need of rebuilding; determining a redundancyvalue based on a difference between the pillar number and the decodethreshold number; determining a slice risk value based on a differencebetween the redundancy value and the number of encoded data slices inthe set of encoded data slices that are in need of rebuilding;determining storage unit reliability of a set of storage units of theDSN that is storing the set of encoded data slices; generating a loss ofdata risk indication based on the slice risk value and the storage unitreliability; and when the loss of data risk indication is above athreshold, placing one or more encoded data slices of the set of encodeddata slices that are in need of rebuilding in the first group of encodeddata slices.
 5. The method of claim 1, wherein the rebuilding furthercomprises: determining, by the rebuilding module, whether the time torebuild the first group of encoded data slices will exceed a priorityrebuild time threshold; when the time to rebuild the first group ofencoded data slices will exceed the priority rebuild time threshold,allocating, by the rebuilding module, a sub-group of the first group ofencoded data slices to a second rebuilding module for rebuilding,wherein the second rebuilding module operates on the first computingdevice, the second computing device, the third computing device, or afourth computing device of the one or more computing devices.
 6. Themethod of claim 1, wherein the rebuilding prioritization protocolcomprises one of: rebuilding the first group of encoded data slicesbefore rebuilding the second group of encoded data slices; rebuildingthe first and second group of encoded data slices in an imbalanced roundrobin manner that favors rebuilding the first group of encoded dataslices; and rebuilding the first and second group of encoded data slicesin accordance with an anti-starvation protocol.
 7. The method of claim 1further comprises: when an encoded data slice has been in the secondgroup of encoded data slices for a predetermined period of time,re-analyzing the encoded data slice based on the rebuildingprioritization function to determine whether the encoded data sliceshould be moved to the first group of encoded data slices; and whendetermined to move the encoded data slice to the first group of encodeddata slices, transferring the encoded data slice to the first group ofencoded data slices.
 8. The method of claim 1 further comprises:transferring, by the analyzing module, a third group of encoded dataslices in the first level rebuilding queue into a third priorityrebuilding queue based on the analyzing, wherein the second rebuildingpriority queue has priority over the third priority rebuilding queue;and rebuilding, by the rebuilding module, the first, second, and thirdgroup of encoded data slices based on a rebuilding prioritizationprotocol.
 9. A computer readable memory device comprises: a first memorysection that stores operational instructions that, when executed by oneor more computing devices in a dispersed storage network (DSN), causes ascanning module of a first computing device of the one or more computingdevices to: scan, from one or more plurality of sets of encoded dataslices to other one or more plurality of sets of encoded data slices, toidentify encoded data slices that are in need of rebuilding; add theidentified encoded data slices into a first level rebuilding queue; asecond memory section that stores operational instructions that, whenexecuted by the one or more computing devices, causes an analyzingmodule of the first computing device or a second computing device of theone or more computing devices to: analyze the identified encoded dataslices in the first level rebuilding queue based on a rebuildingprioritization function to establish a prioritization for at least someof the identified encoded data slices in the first level rebuildingqueue; transfer a first group of encoded data slices in the first levelrebuilding queue into a first priority rebuilding queue based on theanalyzing; transfer a second group of encoded data slices in the firstlevel rebuilding queue into a second priority rebuilding queue based onthe analyzing, wherein the first rebuilding priority queue has priorityover the second priority rebuilding queue; and a third memory sectionthat stores operational instructions that, when executed by the one ormore computing devices, causes a rebuilding module of the firstcomputing device, the second computing device, or a third computingdevice of the one or more computing devices to: rebuild the first andsecond group of encoded data slices based on a rebuilding prioritizationprotocol.
 10. The computer readable memory device of claim 9, whereinthe first memory section further stores operational instructions thatcauses the scanning module to scan by: sending list requests to storageunits of the DSN, wherein the list requests include a request to listslice names of encoded data slices being stored by the respectivestorage units; receiving list responses from the storage units, whereinthe list responses includes a list of slices names of encoded dataslices that are stored by the respective storage units; and interpretingthe list of slices names of encoded data slices that are stored by therespective storage units to identify the encoded data slices that are inneed of rebuilding.
 11. The computer readable memory device of claim 9,wherein the rebuilding prioritization function comprises: a loss of datarisk analysis function that is executed on a set of encoded data slicesby set of encoded data slices basis.
 12. The computer readable memorydevice of claim 11, wherein the third memory section further storesoperational instructions that causes the rebuilding module to rebuildby: for a set of encoded data slices of the one or more plurality ofsets of encoded data slices or of the other one or more plurality ofsets of encoded data slices: determining a pillar number, a decodethreshold number, a number of encoded data slices in the set of encodeddata slices that are in need of rebuilding; determining a redundancyvalue based on a difference between the pillar number and the decodethreshold number; determining a slice risk value based on a differencebetween the redundancy value and the number of encoded data slices inthe set of encoded data slices that are in need of rebuilding;determining storage unit reliability of a set of storage units of theDSN that is storing the set of encoded data slices; generating a loss ofdata risk indication based on the slice risk vale and the storage unitreliability; and when the loss of data risk indication is above athreshold, placing one or more encoded data slices of the set of encodeddata slices that are in need of rebuilding in the first group of encodeddata slices.
 13. The computer readable memory device of claim 9, whereinthe third memory section further stores operational instructions thatcauses the rebuilding module to rebuild by: determining whether the timeto rebuild the first group of encoded data slices will exceed a priorityrebuild time threshold; when the time to rebuild the first group ofencoded data slices will exceed the priority rebuild time threshold,allocating a sub-group of the first group of encoded data slices to asecond rebuilding module for rebuilding, wherein the second rebuildingmodule operates on the first computing device, the second computingdevice, the third computing device, or a fourth computing device of theone or more computing devices.
 14. The computer readable memory deviceof claim 9, wherein the rebuilding prioritization protocol comprises oneof: rebuilding the first group of encoded data slices before rebuildingthe second group of encoded data slices; rebuilding the first and secondgroup of encoded data slices in an imbalanced round robin manner thatfavors rebuilding the first group of encoded data slices; and rebuildingthe first and second group of encoded data slices in accordance with ananti-starvation protocol.
 15. The computer readable memory device ofclaim 9, wherein the second memory section further stores operationalinstructions that causes the analyzing module to: when an encoded dataslice has been in the second group of encoded data slices for apredetermined period of time, re-analyze the encoded data slice based onthe rebuilding prioritization function to determine whether the encodeddata slice should be moved to the first group of encoded data slices;and when determined to move the encoded data slice to the first group ofencoded data slices, transfer the encoded data slice to the first groupof encoded data slices.
 16. The computer readable memory device of claim9 further comprises: the second memory section further storesoperational instructions that causes the analyzing module to: transfer athird group of encoded data slices in the first level rebuilding queueinto a third priority rebuilding queue based on the analyzing, whereinthe second rebuilding priority queue has priority over the thirdpriority rebuilding queue; and the third memory section further storesoperational instructions that causes the rebuilding module to: rebuildthe first, second, and third group of encoded data slices based on arebuilding prioritization protocol.